A conventional mineral processing technique for separating sulphide minerals from an ore rich in magnesium minerals involves the following steps:                (i) crushing and wet milling of the ore to form a pulp having particles of a desired particle size distribution;        (ii) adding frother, collector and depressant to the pulp;        (iii) adding acid to the pulp;        (iv) adding an activator to the pulp; and        (v) flotation of the pulp in one or more stages wherein the sulphide minerals are separated from gangue minerals.        
The addition of collector makes the sulphide minerals hydrophobic and the addition of depressant minimises the recovery of gangue materials to the flotation concentrate. The addition of acid and activator enhances the effect of the collector and, in turn, improves the recovery and/or the grade. The flotation concentrate of valuable sulphide minerals is filtered and dried in preparation for smelting, or other secondary treatment processes such as leaching. For smelting or for other secondary processing, the amount of gangue, particularly magnesium bearing gangue, should be minimised.
It is generally known that improved activity of valuable sulphide minerals and reduced recovery of gangue can be obtained by adding acid to lower the pH or by adding an activator such as copper sulphate. Unfortunately, for many magnesium bearing ores, the addition of acid or activator is relatively ineffective. Often to obtain any discernible improvement, large amounts of acid or activator have to be added and the economic benefits are, more often than not, out-weighed by the cost of the reagents. This is particularly so for nickel ores containing large amounts of magnesium bearing minerals.
A number of strategies have been employed to reduce the consumption of acid and activator including:                (i) making a sand/slime separation at a cut size of about 10 micron and adding acid and activator to the sands fraction (nominally +10 micron) only which contains less fine magnesium bearings minerals than the slimes fraction (nominally −10 micron), or        (ii) adding acid and activator to low volume, high value streams only such as cleaner feed or recleaner feed.        
These strategies tend to be relatively ineffective and their applications are restricted, or the benefits are limited or both. For example, both acid and activator have little effect when added to a sands stream of over 10 micron at the Mt Keith, Western Australia, concentrator of WMC Resources Limited which treats a low grade nickel sulphide ore high in magnesium bearing minerals.